Electronic measuring unit

ABSTRACT

The electronic measuring unit is a logic controlled system which is programmed by a clock control unit. A unit for producing a digital output indicative of a function to be measured is connected to feed a read up and down counter and indicator unit. This counter and indicator unit has the capability to provide an indication of the difference between a previous measurement and one or more subsequent measurements, the value of a single measurement, the difference between a measurement and a preset value, or the value of only a portion of a total value applied to a measuring sensor for the measuring unit. Additionally, the electronic measuring unit is adapted to automatically round off value indications and to zero itself when drift within predetermined limits occurs.

United States Patent Henderson et al.

[451 May 23, 1972 [54] ELECTRONIC MEASURING UNIT 72 Inventors: Robert M.Henderson, Williams Bay; Richard Zechlin; Lowell E. Miller, both ofBeloit, all of Wis.

[73] Assignee: Fairbanks Morse Inc., New York, NY.

[22] Filed: Oct. 17, 1969 [21] Appl. No.: 867,140

[52] US. Cl ..235/15l.3, 235/151.33, 235/92, 177/25 [51] Int. Cl. ..G06f7/46 [58] FieldofSearch ..235/l51.3, 151.33,92 MT, 92 WT, 235/92 EV,183; 177/3, 7, 17, 25, 211

[56] References Cited UNITED STATES PATENTS 3,439,524 4/1969 Rogers..235/l5l.33X

Primary Examiner--Malcolm A. Morrison Assistant Examiner-Edward J. WiseAttorney-Daniel W. Sixbey ABSTRACT The electronic measuring unit is alogic controlled system which is programmed by a clock control unit. Aunit for producing a digital output indicative of a function to bemeasured is connected to feed a read up and down counter and indicatorunit. This counter and indicator unit has the capability to provide anindication of the difference between a previous measurement and one ormore subsequent measurements, the value of a single measurement, thedifference between a measurement and a preset value, or the value ofonly a portion of a total value applied to a measuring sensor for themeasuring unit. Additionally, the electronic measuring unit is adaptedto automatically round off value indications and to zero itself3,378,676 4/1968 Clement ..235/151.3 when d ift within predeterminedlimits occum 3,375,357 3/1968 Dekker et a1. ,235/151.33 X 3,393,3027/1968 Cichanowicz et a] ..235/l5 l .33 64 Claims, 16 Drawing FiguresAnalog To Dlgilal 7 Read Up And Down Counter And Display System 44Measuring lJnit 3.224

- 1m n32 28 Control Automatic Dynamic Zero Test IP40 Zero Set pn qrSomme Control Ramp Clock Number N 391 Rate Frequency Flip Flop ControlDetector Latch 38 OSClllfllOl '2 Control A 8 20 Patented May 23, 19723,665,169

15 Sheets-Sheet 5 l20e I36e Read Up Read Down Tore Switch Visual DisplayVisual Display INVENTORS Robert M. Henderson BY Ric/70rd Ze hll'n Lowe/lE Miller ISM w 84;

ATTORNEY L "IO4 l I INVENTOR5 Robert M. Henderson Richard Zach/in [Ewe/lE. jlf/ler Ma) 46'; ATTORNEY --Nurnber Buffer 15 Sheets-Sheet 8 2 N26com 6 39? Q E mmm ZA ZC GATE F E mmm 6 Patented May 23, 1972 PatentedMay 23, 1972 15 Shets-Sheet 9 mmm wmm

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1. m 282 01. 0 9 M 2U u CF INVENTORS Robert M. Henderson BY Richard Z ech/in r% 8 Mwvl E. M R $0 w w m Patented May 23, 1972 15 Sheets-Sheet 11F (D LIJ O I! lLI N AUTOMATIC ZERO T EST INVENTORS Robert M. HendersonRichard 1 29 ch/in .Lowel/ E. Mil/er 5M NJ ATTORNEY Patented May 23,1972 3,665,169

15 Sheets-Sheet 12 lllllllll I320 l32b I34b l34c I I I I I I I I I II II I I I L #180; vIIBbL- -Il8cl --ll8dL -ll8e I30. 130a I30 I30d if |30eI524q I5IILbI 524bFI5IHI3l fi -iggizz iiilj 5 20 TARE CONTROL UNIT 632324 I 284 3 244 I4 UngclIed 42 9, Memory 1 f j a 328 Lmch r SampleControl 276 206 Reset Rate Flip I Romp LU Unit Tens 324 Lotch OscillatorFlop 2:32 Clock Clock I92 494 38 I 272 l 4 F1 9. /3A z External WeighSignal ontrol INVENTOR'S Robert M. Henderson BY Richard Zach/in Lawql/E. Mil/er QMMLW ATTORNEY Patented May 23, 1972 3,665,169

15 Sheets-Sheet 15 RAMPFF Fig. 13 5 IN VENTORS Robert M. Henderson BYRic/70rd Zach/in Lowe/l E. Miller ATTORNEY ELECTRONIC MEASURING UNIT Anumber of electronic measuring systems capable of providing a digitalindication representative of a value to be measured have been developed.These systems are generally limited to a single, specific use; namelythe indication of the value of a single sensed function. Such systemsare not capable of combining a number of successive measuring operationsto indicate comparative values obtained from successive measurements.

All electronic measuring systems are subject to drift due totemperature, mechanical, environmental and other effects inherent insuch systems. It is desirable to provide both manual and automatic meansfor accurately compensating for the effects of such drift.

It is a primary object of the present invention to provide a novel andimproved electronic measuring unit capable of providing comparativemeasurement indications during two or more successive measuring cycles.

Another object of the present invention is to provide a novel andimproved electronic measuring unit operative in response to programcontrol logic signals from a central clock control unit.

- A further object of the present invention is to provide a novel andimproved electronic measuring unit which is adapted to indicate portionsof a total sensed value which are added to said sensed value duringsuccessive measuring operations while maintaining the total value ofsaid portions.

Another object of the present invention is to provide a novel andimproved electronic measuring unit which is adapted to compare valuesobtained during successive measurements.

A further object of the present invention is to provide a novel andimproved electronic measuring unit which may be manually set to andwhich thereafter automatically deducts the value indicated prior tozeroing from that obtained subsequent to zeroing.

Another object of the present invention is to provide a novel andimproved electronic measuring unit which will automatically zero tocompensate for drift within predetermined ranges.

A further object of the present invention is to provide a novel andimproved electronic measuring unit which is adapted to automaticallyround off an indicated value to a nearest predetermined indication.

Another object of the present invention is to provide a novel andimproved electronic measuring unit adapted to take a plurality ofmeasurements during each measuring cycle and having means to adjust thetime of such measurements to minimize inherent errors due to inputoscillations.

A further object of the present invention is to provide a novel andimproved electronic measuring unit which includes input means tominimize A.C. variations in an input signal.

Another object of the present invention is to provide a counter andindicator system for an electronic measuring unit which includes asensing and control unit for sensing the most significant digitregistered in a counter unit for said system and providing a controlsignal dependent upon the occurrence or non occurrence of a transitionof said most significant digit to cause said system to provide an outputwhich is indicative of the actual numerical value entered in saidcounter unit or the complement thereof.

A further object of the present invention is to provide a novel andimproved electronic measuring unit having a counter and indicator systemadapted to store an indication representative of a previously measuredvalue for subsequent comparison or indication.

A still further object of the present invention is to provide a noveland improved electronic measuring unit having means to enter a manuallypreset value into a counter and indicator unit therefor to be deductedfrom a subsequently measured value.

Other objects, features and attendant advantages of this invention willbecome apparent from a consideration of the following description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a basic block diagram illustrating the major components of theelectronic measuring unit of the present invention;

FIG. 2 is a detailed block diagram of the electronic measuring unit ofthe present invention;

FIG. 3 is a block diagram of the read up and down counter and displayunit for the electronic measuring unit of the present invention;

FIG. 4 is a schematic diagram of the RUAD unit for the read up and downcounter and display unit of FIG. 3;

FIG. 5 is a schematic diagram of the zero set latch and sample rateoscillator of FIG. 1;

FIG. 6 is a schematic diagram of the ramp frequency control of FIG. 1;

FIG. 7 is a schematic diagram of the clock control of FIG. 1;

FIG. 8 is a schematic diagram of the tare control of FIG. 1;

FIG. 9 is a schematic diagram of the number detector of FIG. 1;

FIG. 10 is a schematic diagram of the automatic zero set unit of FIG. 1;

FIG. 11 is a schematic diagram of the zero test unit of FIG. 1;

FIG. 12 is a block diagram of a second embodiment of the zero test unitand automatic zero set unit of the present invention;

FIGS. 13a and 13b comprise a detailed block diagram of a secondembodiment of the electronic measuring unit of the present invention;

FIG. 14 is a block diagram of the zero loop counter section of FIG. 13;and

FIG. 15 is a circuit diagram of the automatic zeroing unit of FIG. 12.

The novel electronic measuring system of the present invention basicallyconstitutes a clock controlled measuring system which is programmedthrough a sequence of operations by a clock control circuit. The programfollowed by the measuring system may be expeditiously altered by theoperation of simple control mechanisms to adapt the system operation fora new function. For purposes of description, the programmed functions ofthe electronic measuring system of this invention will be classifiedinto four major catagories; namely, zero set operation, not zero setoperation, tare setting, and automatic clamping.

The zero set operation of the electronic measuring system is a pushbutton activated function, although an automatic zero set system tocorrect measuring system drift will be subsequently described as ameasuring system component. The manual zero set operation provides theability to zero the system by activation of a single push button. Inzero set operation, the system senses an input function and registersthis function in the form of a positive digital number. This inputfunction is then remembered, however, as the complement of the digitalnumber, and prior to the accomplishment of a subsequent measurement bythe system, the number complement is placed in a novel counterarrangement. Then, as the system takes a subsequent measurement during anot zero set operation, it must count toward 0 until the prior storedfunction is counted out, and then continue to count through 0 for apositive indication. Thus it is seen that in zero set operation, theelectronic measuring system of the present invention simply takes themeasurement of an existing function present at the input to the systemand stores this information so that the stored value may be deductedfrom values obtained from subsequent measurements to be taken.

The ability of the system to accomplish a push button zero set operationwhile remembering a previously measured value adapts the system for awide variety of measuring uses. For example, a plurality of individualmeasurements may be taken without losing the total measurement resultingfrom the successive individual measurements. Applying this principal toa weighing application, the weights of individual packages may bedetermined as they are added to a partially loaded pallet withoutremoving the pallet from the weigh platform for each measurement. Theprocess employed is to use the zero set button to re-zero the systemwith the addition of each package, thereby obtaining the weight of theadded package only. However, totals of each individual package added maybe obtained from a normal electronic accumulator.

In another application, the zero set operation may be used for downmeasurements. Applying this to a weighing application, down weighing maybe accomplished by zero setting the system when the full weight of aplurality of parts is applied to the weigh platform. When the weight isremoved, the count toward 0 from the zero set complement never reachesor passes through zero. For example, in zero set with an applied load of485.50 lbs., the removal of 25 lb. weight will cause the system to counttoward 0, but only to 460.50 lbs. and to indicate minus 25 lbs. Bycoupling the down-weighing concept to push button zero set, anincremental reduction in weight can be obtained. Such a system is usefulin obtaining measurements, such as fuel rates for diesel or gasolineengines.

The tare function of the measuring system is accomplished incoordination with the zero set function, and may occur during a zero setoperation. The tare function permits an operator to manually insert aknown value into the system for future comparison with values to besubsequently measured. For example, in a weighing system, the tarecontrol could be employed to set the weight of containers for materialto be weighed into the system. If the weight of such containers isentered as the complement of the weight value, the system must counttoward 0 until this weight is counted out, and only the actual weightwithin the container will be finally indicated.

In the not zero set operation of the measuring system, the system willmeasure the difference between a measurement formerly taken and anexisting measurement. The not zero set function can be employed toindicate a measurement which is greater than 0, a measurement which isless than 0, a measurement which is greater than 0 but less than someminimum amount, or a measurement which is less than 0 but greater thansome minimum amount.

Finally, the automatic clampingfunction of the measuring system can beemployed to provide a continuous indication of zero when the measuringsystem receives no input. Sometimes, because of drift, the no inputindication will read other than 0, although the drift is small. Insimple terms, the zero clamping system incorporated within the measuringsystem of the present invention looks at all digits recorded in acounter system above the least significant digit to see if they are 0when no measurement is being taken. It also looks at the leastsignificant digit and determines whether it is lower in value than apre-chosen number. When this condition exists, it makes all numbers inthe output indicator for the counter system read 0, even though a smalldrift has occurred.

Zero clamping is employed in cooperation with an automatic zero set unitto accomplish continuous zero adjustment to overcome the problem ofdrift from 0 between push button zero adjustments. Although the pushbutton zero set operation of the measuring system is advantageous inthat it removes the element of operator judgement as to whether he hasset 0 precisely into the system, it does not overcome the problem ofdrift between zero adjustments. The continuous automatic zero feature ofthis system uses the features of push button zeroing and zero clamp in aunique manner to obtain continuous zeroing. For example, after pushbutton zero set has been accomplished to initially zero the system, anot zero set measuring cycle is initiated to accomplish a measurement.It is obvious that if no input to the system is forthcoming, theresultant indication should be 0. In practice, however, this is notprecisely true, for the electronic system will have possibly driftedfrom 0 a slight amount. At this point, the zero clamp is used. If theresultant is sufficiently close to 0 to actuate the zero clamp, then thezero set cycle will be automatically initiated to rezero the system atthis slightly different, new value, thus continuously adjusting for zerodrift.

The operational functions of the electronic measuring system of thepresent invention will be better understood from the subsequentdescription of the system and its operation. GENERAL MEASURING SYSTEMReferring now to the drawings, FIG. 1 constitutes a simplified blockdiagram of the electronic measuring system of the present inventionwhich is employed to illustrate the general system construction andoperation. The electronic measuring system indicated generally at 10includes a sample rate oscillator 12, which may constitute a freerunning oscillator with internal control or an oscillator which operatesunder the control of an external signal from an external control unit14. This external control unit may be a sensor or similar controlassociated with the entity to be measured.

The sample rate oscillator 12 is connected to a control flip flop 16,the output of which is connected back to the sample rate oscillator, andalso to a ramp frequency control 18, and a clock control 20. The outputof the ramp frequency control is connected to the clock control 20 andalso to a digital output measuring unit 22 which provides a digitaloutput signal indicative of a quantity to be measured. This outputsignal is directed to a read up and down counter and display system 24.

For purposes of description, the digital output measuring unit will bedescribed as an analog to digitalmeasuring unit which provides a digitaloutput signal indicative of an analog input signal. This is the mostcommon system employed for electronic measuring applications, but it isrecognized that the electronic measuring unit 10 will function with anydigital output measuring unit 22 which will operate in response to acontrol pulse to provide a digital output indicative of a function to bemeasured.

The clock control 20 forms the program control center for the electronicmeasuring unit 10, and operates in accordance with information signalsreceived from various system sources to provide output control signalsto operational units within the system. For example, the clock controlunit 20 receives information signals from a number detector 26 which isconnected to sense predetermined numerical conditions in the read up anddown counter and display system 24.

The clock, control 20 is connected to control numerous functions in theread up and down counter and display system 24, as well as functions ofa dynamic zero test flip flop 28. The dynamic zero test flip flop isconnected to the read up and down counter and display system and also toa zero test unit 30. The zero test unit is connected to the read up anddown counter and display system. Also a tare control unit 32 is con- Inected to the read up and down counter and display system. Additionally,the zero test unit is connected to an automatic zero set unit 36 whichoperates a connection 40 to a zero set latch 38. Also the zero set latchmay be manually connected to the control flip flop by a zero set switch42. The zero set latch 38 is connected to provide control functions tothe read up and down counter and display system, tare control unit 32,and zero test unit 30.

Considering now the general operation of the measuring system 10 of FIG.1, the switch 42 may be closed to initiate zero set operation of themeasuring system. This will trigger the sample rate oscillator 12 intooperation. As previously indicated, the sample rate oscillator may befree running with internal controls.

The sample rate oscillator provides an output to the control flip flop16, which changes state and locks the sample rate oscillator. Also, thechange of state of the control flip flop 16 provides control signals tothe clock control 20 to remove the reset previously applied to the clockcontrol and to set gate circuits therein. Finally, the output from thecontrol flip flop triggers a ramp period oscillator in the rampfrequency control 18, and this ramp period oscillator sets the togglingrate of the clock control 20. Actually, the ramp frequency control unittoggles the clock control at two different rates, with the faster ratebeing present during non-ramping conditions in the analog to digitalmeasuring unit 22.

For purposes of description, the total clock control program provided bythe clock control 20 will be assumed to be a 40 count control programwith each 10th count constituting a transition to a new functionaldivision in the program. Thus, the system will be described inaccordance with the functions accomplished during counts 0-9, 10-19,20-29, and 30-39,

with count 40 terminating the operational cycle of the system. It willof course be understood that other clock count pro grams could beemployed.

During clock division 0-9, the control flip flop 16 locks the samplerate oscillator, provides control signals to the clock control, andtriggers the ramp frequency control as previously described. In responseto operation of the clock control, strobe signals are provided tocounters in the read up and down counter and display system 24, and anyvalue present at the counter inputs is strobed into the counters. If noinput is present, the counters remain at 0. Thus during a 0-9 clockcycle, any tare value which has been set into the tare control 32 isstrobed into the read up and down counter and display system.

When the clock output from the clock control 20 changes from clock 9 to10, the ramp frequency oscillator in the ramp frequency control unit 18is caused to decrease the clock pulse rate and to toggle the analog todigital measuring unit 22 into operation. This unit takes an inputanalog signal indicative of a value to be measured and converts thesignal to a related digital signal. The input analog signal may beprovided by any of a number of known sensing units having an analogoutput signal to an input 44 for the analog to digital measuring unit,and the digital output from the measuring unit is registered in the readup and down counter and display system 24. This measuring operation ofthe analog to digital measuring unit normally occurs during the clockperiod involving clock pulses -19, and for averaging purposes, it ispossible to have each clock pulse trigger an individual measuring cycleof the analog to digital measuring unit.

At the termination of clock pulse 19 during zero set operation, theanalog to digital measuring unit is disabled and the ramp frequencycontrol unit 18 is caused to again initiate clock pulses at the higherfrequency of the clock pulses 0-9. The number detector 26 is disabled,so that no sensing thereby of the value stored in the read up and downcounter and display system occurs.

During clocks 20-29, counter indications are processed in the read upand down counter and display system 24 in a manner to be subsequentlydescribed, and during clock 30-39 the zero set latch 38 is released.Upon the occurrence of clock 40, the lock on the sample rate oscillator12 is removed, the counters in the read up and down counter and displaysystem 24 are reset, and the clock control 20 is reset. The measuringsystem 10 has now completed a zero set cycle. 1

The not-zero set operation of the electronic measuring unit 10 isbasically similar to the zero set operation, with the exception that thenumber detector 26, the dynamic zero test flip flop 28, the zero testunit 30 and the automatic zero set unit 36 may be brought intooperation.

During the 0-9 count of the clock control 20, the compliment of ameasurement value taken during a previous measuring cycle of the analogto digital measuring unit 22 is taken from storage in the read up anddown counter and display system 24 and entered into the countersthereof. Thus, the count taken during the next measuring cycle of theanalog to digital measuring unit 22 must count through the complemententered in the counters for the read up and down counter and displaysystem.

At the end of clock 19 during not-zero set operation, the mostsignificant digit, namely the highest digit, in the counters for theread up and down counter and display system is sensed, and if a changeof state has occurred since clock 10, (from a 9 indication to a 0) thedynamic zero test flip flop 28 changes state. This causes a controlsignal to be sent to the read up and down counter and display systemfrom the dynamic zero test flip flop to cause the number in the countersof this system to be directly displayed instead of the complementthereof.

Additionally, at clock 19, the number detector 26 operates to provide around off function for the indication to be subsequently provided by theread up and down counter and display system 24. The number detectorsenses the output from a counter in the read up and down counter anddisplay system which indicates the first digit behind the decimal pointin the output indication, and if such digit is not either a 0, a 5, orsome similar predetermined number, the number detector causes the clockcontrol 20 to permit another ramp measuring cycle to begin in the analogto digital measuring unit 22. This additional ramp cycle causes digitaloutput pulses from the analog to digital measuring unit to be fed to theread up and down counter and display system 24, and when these pulsestrigger the counter providing the sensed digit to the round off number(i.e., 0 or 5) the number detector permits the clock control to switchto clock 20 terminating the cycle of the analog to digital measuringunit. Thus a rounded number is indicated in the read up and down counterand display system.

During not-zero set operation, the electronic measuring unit 10 may alsoutilize the zero test unit 30 and automatic zero set unit 36 toaccomplish automatic zeroing of the system when no input is present at44. At the end of clock 19, the zero test unit 30 will sense theindication in the counters provided in the read up and down counter anddisplay system 24, and if this indication is within a given band, plusor minus, from the previous zero set operation, the automatic zero setunit 36 will automatically zero the counter output. This automaticzeroing function is exactly the same as the manual zero set functionprovided with the switch 42.

The exact manner in which the circuitry of the present inventionperforms the heretofore described functions will become subsequentlyapparent by reference to the detailed description of the remainingdrawings.

ANALOG TO DIGITAL MEASURING UNIT The analog to digital measuring unitutilized with the present invention may comprise any one of a number ofconventional measuring units which operate to convert an analogelectrical signal indicative of the quantity to be measured to a digitaloutput signal which is a function of the input signal. Generally suchmeasuring units include a reference ramp generator which provides a rampsignal for comparison with the input analog signal, and an oscillatorgenerated digital output signal which is time gated in accordance withthe input analog signal ramp signal comparison.

For purposes of illustration in FIG. 2, the analog to digital measuringunit 22 is formed by a dual ramp system described completely in aco-pending application entitled Measuring and Conversion System, Ser.No. 669,1 l3 assigned to the assignee herein. Briefly, this analog todigital measuring unit employs an analog input signal provided by asensing unit, transducer, or any similar unit 46 capable of producing ananalog signal which is a function of the quantity to be measured. Theanalog input signal may be provided by a plurality of load cells 48 andis developed across load cell resistors 50 and fed to a DC. amplifier 52at the input to the analog to digital measuring unit. Any A.C. componentin the analog input signal, is coupled by a coupling capacitor 54 to anA.C. amplifier 56. This A.C. component is often generated by conditionspresent during the measuring process and normally constitutes anundesirable factor in the analog input signal. For example, in a motionweighing application, the A.C. component can be generated by vibrationsin a weigh platform connected to the load cells.

The output of the A.C. amplifier 56 is developed across an outputresistor 58 and is inverted relative to the output of the DC. amplifier52 which is developed across an output resistor 60. The two outputsignals are combined with a bias signal at the input of a first detector62. The A.C. amplifier may constitute an operational amplifier whichoperates to substantially phase shift the A.C. component of the inputsignal with respect to the DC. component thereof, or conventionalinversion circuitry known to the art may be employed. The A.C.component, although inverted, is maintained unchanged in magnitude, andtherefore the combination of the outputs from the A.C. and DC.amplifiers algebraically reduce oscillatory forces in the input analogsignal.

The first detector 62, which may constitute a zero crossing detector,receives the sum of a negative bias signal which is provided by a biassource 64 across a bias resistor 66, the analog input signal correctedfor A.C. variations, and a positive going ramp signal generated by aramp generator 68 and developed across a first ramp resistor 70. Thealgebraic sum of the positive going ramp and analog signals and thenegative bias signal is applied to the input of the zero crossingdetector, and when the algebraic sum of these signals reaches zero dueto the linearly changing ramp signal, the zero crossing detector outputshifts rapidly to provide a start signal at the input of a count outgate 72. Upon receiving the start signal, the count out gate passesconstant frequency pulses from a stable oscillator 74, these pulsesbeing fed from the output of the count out gate to a divide ten counterin the read up and down counter and display system 24 to be subsequentlydescribed.

As the linear ramp signal is increasing across the first ramp resistor70, the ramp generator is also developing a ramp signal across a secondramp resistor 75 in a second comparison circuit. The signal from thesecond ramp resistor is algebraically compared with a negative biassignal provided by a bias source 76 across a bias resistor 78. When thealgebraic sum of the signals at the input of a second zero crossingdetector 80 reaches zero, the output potential from the second zerocrossing detector changes rapidly in polarity from a negative to apositive value. This rapid change in output potential from the secondzero crossing detector is directed to a gate 82, which in turn operatesto change the state of a ramp control flip flop circuit 84. When theramp control flip flop circuit changes state, it operates to terminatethe feeding of pulses through the count out gate 72 and also to providea stop signal to a ramp control switching circuit 86. This switchingcircuit operates to terminate the action of the ramp generator 68 sothat the ramp signal input to the comparison circuits drops to 0,causing both zero crossing detectors 62 and 80 to return to an initialstate.

The operational cycle of the analog to digital measuring unit 22 isdetermined by the ramp control flip flop 84, which is ac tivated uponthe occurrence of clock 10 from the clock control 20. Clock 10 causes agate 88 to change state and permit the ramp control flip flop to accepttiming pulses from the ramp frequency control 18 at an input 90. Eachtiming pulse causes the ramp control flip flop to trigger the rampcontrol switching circuit 86 to initiate operation of the ramp generator68. Upon the occurrence of clock 20, the gate 88 changes state toprevent the ramp control flip flop from operating further in response totiming pulses at the input 90.

READ UP AND DOWN COUNTER AND DlSPLAY SYSTEM The read up and down counterand display system 24, in conjunction with the clock control 20constitutes the heart of the electronic measuring system 10. Therefore,it is advantageous to consider this system and the subsystems associatedtherewith in detail before embarking upon a detailed study of theremainder of the electronic measuring system.

Referring now to FIGS. 3, and 4 it will be noted that the read up anddown counter and display system 24 includes a plurality of counter andindicator sections 92a, 92b, 92c, 92d and 92a. Each counter andindicator section includes a counter of known type which is adapted toprovide a binary output indication in response to a digital pulse input.Thus a divide ten counter 94e receives the digital output from theanalog to digital measuring unit, and this output is serially fedthrough counters 94d, 94c, 94b, and 94a in the various counter sections,which, for purposes of description, will be considered to constituteseparate decades. It will be noted that count input lines 96 extend fromthe output of each counter to the input of the subsequent counter, sothat the counters are serially connected.

Each counter and indicator section of the read up and down counter anddisplay system 24 is substantially similar in construction to theremaining sections, and therefore, the section 92d at the far left ofFIG. 3, which provides an indication of the most significant digitmeasured, will be described and shown in detail. It will be recognized,that the description of this section applies to the remaining sectionsand like reference numerals may be employed. Some differences occurbetween counter and indicator sections, particularly in the last twodecades at the right hand side of FIG. 3 which provide the leastsignificant digits in the output indication. These differences will besubsequently described.

Each counter and indicator section includes, in addition to the countinput line, a strobe control line 98 which permits selective strobing ofeach counter by strobe input signals. It will be noted that the divideten counter 94e is provided with a separate strobe control line 98e anda reset line 100.

Also, each counter with the exception of the divide ten counter isadapted to receive a four place binary input over four input lines 102extending from a tare switch gate 104 which is in turn connected to atare switch 106. Additional binary inputs to each counter may beprovided by a complement memory gate 108 connected to the four inputlines for each counter. The input lines 102e for the divide ten counter94e are connected only to the associated complement memory gate l08e.

The output from each counter is provided in the form of a four digitbinary number over four outputs 110, individually designated A, B, C, &D, to a read up and down unit (RUAD) l 12.

The counters each incorporate direct set inputs 102, and with a strobesignal at 0 on the strobe line 98, the logic level on the inputs 102will appear on corresponding counter outputs 110. With a 0 reset signalon the reset line 100, the counter outputs 110 will all zero regardlessof strobe and clocking of the counter.

The most significant binary digit on the output line D of the counterand indicator section 920 may be sensed by means of a dynamic zerotransition line 114 for a purpose to be subsequently described. Thesection 92a differs in this respect from the remaining sections whichprovide output indications of lesser significance.

The purpose of each, RUAD unit 112 is to enable the read up and downcounter and display system 24 to store initial zero set information, toprovide a read out indication of measuring inputs to the electronicmeasuring system 10 which are of a lesser value than a stored, initialzero set value, and to retain the ability to read out indications whichare greater in value than the initial zero set value. Therefore, a fourdigit binary output is provided from each RUAD unit along output lines116 individually designated A, B, C and D to a visual display memoryunit 118 and also to a counter compliment memory unit 120. Additionally,each output from the RUAD unit in a counter and display section may besampled by four zero test lines 122 connected thereto.

The RUAD unit 112 operates in response to a RUAD control signal providedat a control input 124 thereof, as will be better understood withreference to FIG. 4. The RUAD unit associated with a counter outputincludes a Hex inverter 126 adapted to provide output signals which arethe inverse of the binary input signals provided thereto (OUT equal l NThe inputs to the Hex inverter constitute the outputs on lines A, B, C &D from an individual counter plus the RUAD control input 124. The Hexinverter incorporates inverter sections A, B, C, D, & E for each ofthese inputs, and the outputs of the Hex inverter are connected to afour circuit Exclusive OR unit 128. The output of this Exclusive OR unitis l if one input thereto is l and the other 0." It is the outputs fromthe Exclusive OR unit which form the outputs A, B, C and D from the RUADunit 112 to the visual display memory unit 118 and the countercompliment memory unit 120.

The components of the RUAD unit 112 in FIG. 4 have been provided withpin numbers, and the operation of this RUAD unit will be readilyunderstood by referring to the following truth tables wherein said pinnumbers are used for purposes of description:

1. An electronic measuring unit comprising measuring means adapted toprovide a measurement output signal which is a function of a quantity tobe measured, count indication means to receive and register themeasurement output signal from said measuring means, said countindication means including counter means operative in response to saidmeasurement output signal to register a numerical value indicative ofsaid measurement output signal, and output control means connected toreceive an output from said counter means, said output control meansoperating in response to control signals received thereby to selectivelyprovide an output representing either the numerical value registered bysaid counter means or a complement thereof, control signal source meansconnected to provide control signals to control said output controlmeans, and zero set control means operative to cause said control signalsource means to cause said output control means to provide an outputrepresenting only the complement of the numerical value registered bysaid counter means.
 2. The electronic measuring unit of claim 1 whereinsaid count indication means includes memory means connected to receivethe output from said output control means, said memory means beingoperative to store said output and to selectively provide said storedoutput to the input of said counter means.
 3. The electronic measuringunit of claim 2 wherein said count indication means includes indicatormeans connected to receive the output from said output control means,said indicator means being selectively operable to provide an indicationrepresenting the value of said output from said output control means,and said zero set control means is connected to control said outputcontrol means and being operable to cause said indicator means to retaina previous indication regardless of the presence of an output from saidoutput control Means, said zero set control means being operable tocause said output control means to provide an output representing onlythe complement of the numerical value registered by said counters tosaid memory means.
 4. The electronic measuring unit of claim 2 whichincludes control means operative to cause said memory means to providethe output of said output control means stored thereby during a previousoperational cycle of said measuring unit to the input of said countermeans for combination with a measurement output signal occurring duringa subsequent operational cycle.
 5. The electronic measuring unit ofclaim 1 wherein a manually operable switch is connected to activate saidzero set control means.
 6. The electronic measuring unit of claim 1wherein said output control means is operative to provide the ninescomplement of the numerical value registered by said counter means. 7.The electronic measuring unit of claim 1 wherein said zero set controlmeans includes zero test means connected to said count indication meansto sense digits registered thereby as a result of said measurementoutput signal, said zero test means operating when said sensed digitsfall within a predetermined range of numerical values to initiateoperation of said control signal source means.
 8. An electronicmeasuring unit comprising measuring means adapted to provide ameasurement output signal which is a function of a quantity to bemeasured during a measurement cycle, count indication means connected toreceive and register a digital value indicative of the measurementoutput signal from said measuring means and number detector meansconnected to said count indication means to sense at the end of saidmeasurement cycle a digit registered thereby as a result of saidmeasurement output signal, said number detector means operating whensaid sensed digit is other than a predetermined value to cause a signalto be fed to said count indication means to alter the value registeredby said count indication means to said predetermined value.
 9. Theelectronic measuring unit of claim 8 wherein said number detector meansoperates in response to a sensed digit of a value other than that ofsaid predetermined value to cause said measuring means to provide ameasurement output signal to said count indication means to alter saidsensed digit to said predetermined value.
 10. The electronic measuringunit of claim 9 wherein the measurement output signal from saidmeasuring means to said count indication means constitutes pulse signalsindicative of the function to be measured, said number detector meansoperating upon the termination of said pulse signals and in response toa sensed digit at the output of said output control means of a valueother than said predetermined value to cause said measuring means toreinitiate a pulse output signal to said count indication means untilsaid count indication means registers said predetermined value.
 11. Inan electronic measuring unit wherein sensing means provide an inputelectrical signal which is a function of a quantity to be measured to ameasuring means operative during a measuring cycle to provide an outputindicative of the amplitude of said input electrical signal, a methodfor reducing the effects resulting from the natural frequency ofvibration of said sensing means which includes initiating a plurality ofsuccessive measuring cycles for each single measurement operation toobtain a number of output measurement indications and initiating atleast one initial measuring cycle of said measurement operation at anypoint on a first excursion of the natural frequency curve of saidsensing means and to thereafter alternately initiate subsequentmeasuring cycles for said measuring operation at points on alternatingopposed excursions of said natural frequency curve substantiallycorresponding to the cycle initiation points on said first excursion.12. The method of claim 11 wherein a plurality of successive measuringcycles are initiated at A plurality of points on said first excursion,an equal number of measuring cycles being initiated at substantiallycorresponding points on alternating opposed excursions occurringsubsequent to said first excursion.
 13. A method for cumulativeelectronic measuring which includes obtaining a decimal code signalwhich is a function of a first value and indicative of a numerical valuetherefor, converting said first decimal code signal to provide a seconddecimal code signal indicative of the complement of said first decimalcode signal, obtaining a second value indicative of a quantitysubsequently measured, combining said second decimal code signal withsaid second value to provide a third decimal code signal indicative ofthe difference between said first and second values, sensing the mostsignificant digit in said third decimal code signal to determine theoccurrence of a transition therein during the formation of said thirddecimal code signal, and converting said third decimal code signal toprovide a fourth decimal code signal indicative of the complement ofsaid third decimal code signal upon the non-occurrence of suchtransition.
 14. In an electronic measuring system for sensing a quantityand providing an electrical measurement signal indicative of the valueof said quantity to create a numerical indication thereof in anindicator system, a method for cumulatively comparing values obtainedduring a plurality of successive measuring operations which includesobtaining a first electrical measurement signal during an initialmeasuring operation, maintaining a previous indication on said indicatorsystem in the presence of said first measurement signal while storingthe complement of said first measurement signal, obtaining a secondmeasurement signal during a second measuring operation, employing saidsecond measurement signal with the complement of said first measurementsignal to obtain a difference signal, electrically sensing whether thevalue indicated by said first measurement signal is greater or less thanthe value indicated by said second measurement signal, and storing saiddifference signal for use with a subsequent measuring signal to obtain asignal indicative of the value difference therebetween, a signalindicative of a value which is the complement of the value indicated bysaid difference signal being stored when said first measurement signalis indicative of a value which exceeds the value indicated by saidsecond measurement signal.
 15. In an electronic measuring system forsensing a quantity and providing an electrical measurement signalindicative of the value of said quantity to create a numericalindication thereof in an indicator system, a method for cumulativelycomparing values obtained during a plurality of successive measuringoperations which includes obtaining a first electrical measurementsignal during an initial measuring operation, maintaining a previousindication on said indicator system in the presence of said firstmeasurement signal while storing said first measurement signal,obtaining a second measurement signal during a second measuringoperation, employing said second measurement signal with said firstmeasurement signal to obtain a difference signal, storing saiddifference signal for use with a subsequent measurement signal to obtaina subsequent difference signal, and providing said difference signal tosaid indicator system to obtain a numerical difference indication. 16.An electronic measuring unit comprising measuring means adapted toprovide a measurement output signal which is a function of a quantity tobe measured, count indication means including counter means operative inresponse to said measurement output signal to register a numerical valueindicative of said measurement output signal, and output control meansconnected to receive an output from said counter means, said outputcontrol means operating to selectively provide an output representingeither the numerical value registered by said counter means oR acomplement thereof, and transition sensing means connected to saidcounter means to sense a transition of the most significant digit of thenumerical value registered thereby from a first to a second value as aresult of said measurement output signal, said transition sensing meansoperating to control said output control means by providing a firstcontrol signal to said output control means in response to an occurrenceof such transition and a second control signal to said output controlmeans in response to the non-occurrence of such transition.
 17. Theelectronic measuring unit of claim 16 wherein said output control meansoperates in response to said first control signal to provide an outputrepresenting the numerical value registered by said counter means and inresponse to said second control signal to provide an output representingthe complement of said numerical value.
 18. The electronic measuringunit of claim 16 wherein said count indication means includes memorymeans connected to receive the output from said output control means,said memory means being operative to store said output and toselectively provide said stored output to the input of said countermeans.
 19. The electronic measuring unit of claim 18 which includescontrol means operative to cause said memory means to provide the outputof said output control means stored thereby during a previous operationcycle of said measuring unit to the input of said counter means forcombination with a measurement output signal occurring during asubsequent operational cycle.
 20. The electronic measuring unit of claim19 which includes zero set control means connected to control saidoutput control means, said zero set control means being operative whenactivated to cause said output control means to provide an outputrepresenting only the complement of the numerical value registered bysaid counters to said memory means.
 21. The electronic measuring unit ofclaim 20 which includes zero test means connected to the output of saidoutput control means to sense the digits appearing as a result of themeasurement output signal registered by said counter means, said zerotest means operating when said sensed digits fall within a predeterminedrange of numerical values to initiate operation of said zero set means.22. The electronic measuring unit of claim 21 which includes automaticzeroing means activated by said zero test means when said sensed digitsfall within a predetermined range of numerical values to zero saidcounter means.
 23. The electronic measuring unit of claim 22 whereinsaid zero test means activates said automatic zeroing means when saidsensed digits fall within a first predetermined range of numericalvalues and activates said zero set control means when said sensed digitsfall within a second predetermined range of numerical values, saidsecond range of the numerical values differing from said first range.24. The electronic measuring unit of claim 19 which includes zero testmeans connected to said count indication means to sense digitsregistered thereby as a result of said measurement output signal, andautomatic zeroing means activated by said zero test means when saidsensed digits fall within a predetermined range of numerical values tozero said counter means.
 25. The electronic measuring unit of claim 16wherein said counter means includes first counter means and secondcounter means connected to receive said measurement output signal, saidsecond counter means being connected to provide an output to said outputcontrol means, said count indication means including memory meansconnected to provide an input to said second counter means and countdown means connected between said first counter means and said memorymeans, said count down means operating to receive an output representingthe numerical value registered by said first counter means and toprovide the complement of such numerical value to said memory means. 26.The electronic measuring unit of clAim 25 wherein said transitionsensing means is connected to said second counter means to sense atransition of the most significant digit registered thereby from a firstto a second value as a result of said measurement output signal.
 27. Theelectronic measuring unit of claim 26 wherein said output control meansoperates in response to said first control signal to provide an outputrepresenting the numerical value registered by said second counter meansand in response to said second control signal to provide an outputrepresenting the complement of said numerical value.
 28. The electronicmeasuring unit of claim 25 which includes number detector meansconnected to the output of said output control means to sense a digit ofthe numerical indication provided thereby, said number detector meansoperating when said sensed digit is other than a predetermined value tocause said measuring means to provide an additional measurement outputsignal to said second counter means to alter said sensed digit to saidpredetermined value, and means to prevent said additional measurementoutput signal from reaching said first counter means.
 29. The electronicmeasuring unit of claim 25 which includes means connected to zero saidsecond counter means, zero test means connected to the output of saidoutput control means to sense when the digits of the numericalindication provided thereby fall within a predetermined range ofnumerical values relative to zero, said zero test means operating whensaid sensed digits fall within said predetermined range to cause saidzeroing means for said second counter means to zero said second countermeans.
 30. An electronic measuring unit comprising measuring meansadapted to provide a measurement output signal which is a function of aquantity to be measured, count indication means to receive and registerthe measurement output signal from said measuring means, said countindication means including counter means operative in response to saidmeasurement output signal to register a numerical value indicative ofsaid measurement output signal, and output control means connected toreceive an output from said counter means, said output control meansoperating to selectively provide an output representing either thenumerical value registered by said counter means or a complementthereof, and number detector means connected to said count indicationmeans to sense a digit registered thereby as a result of saidmeasurement output signal, said number detector means operating whensaid sensed digit is other than a predetermined value to alter the valueof said digit registered by said count indication means to saidpredetermined value.
 31. The electronic measuring unit of claim 30wherein said number detector means operates in response to a senseddigit of a value other than that of said predetermined value to causesaid measuring means to provide a measurement output signal to saidcount indication means to alter said sensed digit to said predeterminedvalue.
 32. The electronic measuring unit of claim 31 wherein themeasurement output signals from said measuring means to said countindication means constitute digital pulse signals, said measuring meansoperating to provide digital pulse output signals which are a functionof the quantity to be measured to said counter means and said numberdetector means operating upon the termination of said digital pulsesignals in response to a sensed digit at the output of said outputcontrol means of a value other than said predetermined value to causesaid measuring means to reinitiate a digital output signal to saidcounter means until said counter means causes the predetermined valuefor said sensed digit to occur at the output of said output controlmeans.
 33. An electronic measuring unit comprising measuring meansadapted to provide a measurement output signal which is a function of aquantity to be measured, count indication means to receive and registerthe measurement output signal from said measUring means, said countindication means including counter means operative in response to saidmeasurement output signal to register a numerical value indicative ofsaid measurement output signal, and output control means connected toreceive an output from said counter means, said output control meansoperating to selectively provide an output representing either thenumerical value registered by said counter means or a complementthereof, zero set control means connected to control said output controlmeans, said zero set control means being operative to cause said outputcontrol means to provide an output representing only the complement ofthe numerical value registered by said counter means and zero test meansconnected to said count indication means to sense digits registeredthereby as a result of said measurement output signal, said zero testmeans operating when said sensed digits fall within a predeterminedrange of numerical values to initiate operation of said zero set means.34. An electronic measuring unit comprising measuring means operativeduring a measuring cycle to provide a measurement output signal which isa function of a quantity to be measured, count indication meansconnected to receive and register the measurement output signal fromsaid measuring means and programming means operable to program saidmeasuring unit during an automatic cycle of operation, said programmingmeans including pulse source means to provide clock control pulses andprogram control means connected to receive said clock control pulses andoperative upon the occurrence of a first number of clock control pulsesto successively activate said measuring means in response to clockcontrol pulses occurring between said first number of clock controlpulses and a second number of clock control pulses to provide aplurality of measuring cycles, said program control means operating uponthe occurrence of said first number of clock control pulses to causesaid pulse source means to change the frequency of the clock controlpulses to provide an elapsed time between clock control pulses greaterthan the time required for one said measuring cycle.
 35. The electronicmeasuring unit of claim 34 wherein said count indication means includescounter means operative in response to said measurement output signal toregister a numerical value indicative thereof, output control meansconnected to receive an output from said counter means, said outputcontrol means operating to selectively provide an output representingeither the numerical value registered by said counter means or acomplement thereof, and memory means connected between said outputcontrol means and the input to said counter means to receive and storethe output from said output control means, said program control meansoperating during the automatic cycle of operation in response to a clockcontrol pulse occurring before the occurrence of said first number ofclock pulses to cause said memory means to provide said stored output tothe input of said counter means.
 36. The electronic measuring unit ofclaim 35 which includes transition sensing means activated by saidprogram control means in response to a clock control pulse occurringafter the occurrence of said second number of clock control pulses, saidtransition sensing means being connected to said counter means to sensea transition of the most significant digit registered thereby from afirst to a second value as a result of said measurement output signaland operative to provide a first control signal to said output controlmeans in response to an occurrence of such transition and a secondcontrol signal to said output control means in response to thenon-occurrence of such transition, said output control means operatingin response to said first control signal to provide an outputrepresenting the numerical value registered by said counter means and inresponse to said second control signal to provide an output representingthe complement of said numerical value.
 37. The electronic measuringunit of claim 36 which includes zero set control means connected tocontrol said output control means, said zero set control means beingoperative to cause said program control means to bypass said transitionsensing means and cause said output control means to provide an outputrepresenting only the complement of the numerical value registered bysaid counters.
 38. The electronic measuring unit of claim 37 whereinsaid count indication means includes indicator means connected toreceive the output from said output control means, said indicator meansbeing selectively activated by said program control means upon theoccurrence of a clock control pulse subsequent to the occurrence of saidsecond number of clock control pulses to provide an indicationrepresenting the value of the output from said output control means. 39.The electronic measuring unit of claim 38 wherein said zero set controlmeans is operative to cause said program control means to bypass saidindicator means whereby said indicator means will not operate to providean indication representing the value of the output from said outputcontrol means.
 40. The electronic measuring unit of claim 39 whichincludes zero test means connected to said count indication means andoperative by said program control means before the operation thereby ofsaid indicator means but subsequent to the occurrence of said secondnumber of clock control pulses to sense digits registered by said countindication means as a result of said measurement output signal, saidzero test means operating when said sensed digits fall within apredetermined range of numerical values to initiate operation of saidzero set means.
 41. In an electronic measuring unit including sensingmeans having a natural frequency of vibration operative to provide anelectrical input signal which is a function of a quantity to be measuredand which varies cyclically in accordance with the opposed excursions ofthe natural frequency of vibration of said sensing means, measuringmeans for receiving said input signal and providing an output during ameasuring cycle which is indicative of the amplitude of said inputsignal, measuring control means for sequentially actuating saidmeasuring means to execute a plurality of sequential measuring cyclesduring a single measuring operation, said control means being operativeto activate said measuring means to initiate at least one initialmeasuring cycle of a measuring operation at any point on a firstexcursion of the natural frequency curve of said sensing means and tothereafter alternately initiate subsequent measuring cycles for saidmeasuring operation at points on alternating opposed excursions of saidnatural frequency curve substantially corresponding to the cycleinitiation points on said first excursion and input signal receivingmeans connected between said sensing means and measuring means to removeAC variations caused by an AC component in said input signal, said inputmeans including means to provide an AC signal corresponding to the ACcomponent in said input signal but inverse thereto for combination withsaid input signal.
 42. A counter and display system for receiving andregistering a number comprising counter means for receiving andregistering said number and providing an output indicative thereof, saidcounter means including a plurality of counter section means, eachoperative to provide an output indicative of one digit of saidregistered number, read up and down output control means connected toreceive the output from said counter means, said read up and down outputcontrol means operating to selectively provide an output representingeither the numerical value registered by said counter means or acomplement thereof and transition sensing means connected to saidcounter means to sense a transition of the most significant digitregistered thereby from a first to a second value, said transitionsensing means operating to provide a first control Signal to said readup and down output control means in response to an occurrence of suchtransition and a second control signal to said read up and down outputcontrol means in response to a non-occurrence of such transition, saidread up and down output control means operating in response to saidfirst control signal to provide an output representing the numericalvalue registered by said counter means and in response to a secondcontrol signal to provide an output representing a complement of saidnumerical value.
 43. The counter and display system of claim 42 whereinmemory means are connected between the output of said read up and downoutput control means and said counter means, said memory means beingoperative to store the output of said read up and down output controlmeans and to selectively provide said stored output to said countermeans, said counter means operating to mathematically combine the storedoutput from said memory means with a number subsequently receivedthereby and to register the result of such combination.
 44. The counterand display system of claim 42 wherein said read up and down outputcontrol means is operative in response to said second control signal toprovide an output representing the nines complement of the numericalvalue registered by said counter means.
 45. An electronic measuring unitcomprising measuring means operative during a measuring cycle to providea measurement output signal which is a function of a quantity to bemeasured, count indication means connected to receive and register themeasurement output signal from said measuring means, said countindication means including first and second counter means operative inresponse to said measurement output signal to register a numerical valueindicative thereof, output control means connected to receive an outputfrom said second counter means, said output control means operating toselectively provide an output representing either the numerical valueregistered by said second counter means or a complement thereof, memorymeans connected to provide an input to said second counter means, andcount down means connected between said first counter means and saidmemory means, said count down means operating to receive an outputrepresenting the numerical value registered by said first counter meansand to provide the complement of such numerical value to said memorymeans, programming means operable to program said measuring unit duringan automatic cycle of operation, said programming means including pulsesource means to provide clock control pulses and program control meansconnected to receive said clock control pulses, said program controlmeans operating in response to said clock control pulses to control theoperation of said measuring and count indication means, and transitionsensing means activated by said program control means and connected tosaid second counter means to sense a transition of the most significantdigit registered thereby from a first to a second value as a result ofsaid measurement output signal, said transition sensing means operatingto provide a first control signal to said output control means inresponse to an occurrence of such transition and a second control signalto said output control means in response to the non-occurrence of suchtransition, said output control means operating in response to saidfirst control signal to provide an output representing the numericalvalue registered by said second counter means and in response to saidsecond control signal to provide an output representing the complementof said numerical value, and said program control means operating uponthe occurrence of a first number of clock pulses to activate saidmeasuring means and after the occurrence of a second number of clockpulses subsequent to the activation of said measuring means to activatesaid transition sensing means.
 46. The electronic measuring unit ofclaim 45 wherein said program control means operates upon the occurrenceof said first nuMber of clock control pulses to successively activatesaid measuring means in response to each clock control pulse occurringbetween said first number of clock control pulses and said second numberof clock control pulses, said program control means operating upon theoccurrence of said first number of clock control pulses to cause saidpulse source means to change the frequency of the clock control pulsesto provide an elapsed time between clock control pulses greater than thetime required for one of said measuring cycles.
 47. The electronicmeasuring unit of claim 46 which includes number detector meansconnected to the output of said output control means and operative uponactivation by said program control means after the occurrence of saidsecond number of clock-control pulses to sense a digit of the numericalindication provided by said output control means, said number detectormeans operating when said sensed digit is other than a predeterminedvalue to cause said measuring means to provide an additional measurementoutput signal to said second counter means to alter said sensed digit tothe predetermined value, said program control means including gatingmeans to prevent said additional measurement output signal from reachingsaid first counter means.
 48. The electronic measuring unit of claim 47which includes zeroing means connected to zero said second countermeans, zero test means connected to the output of said output controlmeans and operative upon activation by said program control means afterthe occurrence of said second number of clock control pulses to sensewhen the digits of the numerical indication provided by said outputcontrol means fall within a predetermined range of numerical valuesrelative to 0, said zeroing means being connected to said zero testmeans and transition sensing means for operation when said digits sensedby said zero test means fall within said predetermined range and saidtransition sensing means senses a transition of the most significantdigit to provide a zeroing signal to said second counter means, saidtransition sensing means operating to render said zeroing meansinoperative when said transition sensing means fails to sense atransition of the most significant digit to permit alteration of saidsecond counter means by said number detector means.
 49. The electronicmeasuring unit of claim 46 which includes zeroing means connected tozero said second counter means, zero test means connected to the outputof said output control means and operative upon activation by saidprogram control means after the occurrence of said second number ofclock control pulses to sense when the digits of the numericalindication provided by said output control means fall within apredetermined range of numerical values relative to 0, said zeroingmeans being connected to said zero test means and transition sensingmeans for operation when said digits sensed by said zero test means fallwithin said predetermined range and said transition sensing means sensesa transition of the most significant digit to provide a zeroing signalto said second counter means.
 50. The electronic measuring unit of claim46 which includes zero set control means operative to permit a count tobe registered by said first counter means and entered in said memorymeans, said count indication means including indicator means connectedto receive the output from said output control means, said indicatormeans being selectively activated by said program control means upon theoccurrence of a clock control pulse subsequent to the occurrence of saidsecond number of clock control pulses to provide an indication of thevalue of the output from said output control means, said zero setcontrol means operating to prevent said indicator activation by saidprogram control means.
 51. An electronic measuring unit comprisingmeasuring means adapted to provide a measurement output signal which isa function of a quantity to be measured, count indication Means toreceive and register the measurement output signal from said measuringmeans, said count indication means including counter means operative inresponse to said measurement output signal to register a numerical valueindicative of said measurement output signal, and output control meansconnected to receive an output from said counter means, said outputcontrol means operating to selectively provide an output representingeither the numerical value registered by said counter means or acomplement thereof, zero test means connected to said count indicationmeans to sense digits registered thereby as a result of said measurementoutput signal, and automatic zeroing means activated by said zero testmeans when said sensed digits fall within a predetermined range ofnumerical values to zero said counter means.
 52. The electronicmeasuring unit of claim 51 which includes zero set control meansconnected to control said output control means, said zero set controlmeans being operative to cause said output control means to provide anoutput representing only the complement of the numerical valueregistered by said counters, said zero test means operating when saidsensed digits fall within a predetermined range of numerical values toinitiate operation of said zero set means.
 53. The electronic measuringunit of claim 52 wherein said zero test means activates said automaticzeroing means when said sensed digits fall within a first predeterminedrange of numerical values and activates said zero set control means whensaid sensed digits fall within a second predetermined range of numericalvalues, said second range of numerical values differing from said firstrange.
 54. An electronic measuring unit comprising measuring meansadapted to provide a measurement output signal which is a function of aquantity to be measured during a measurement cycle, count indicationmeans connected to receive and register a digital value indicative ofthe measurement output signal, zero test means connected to said countindication means to sense the digits registered by said count indicationmeans at the end of said measurement cycle, and automatic zeroing meansactivated by said zero test means when said sensed digits fall within apredetermined range of values to provide a signal to zero said countindication means.
 55. The electronic measuring unit of claim 54 whichincludes number detector means connected to said count indication meansto sense subsequent to said measurement cycle a digit registered therebyas a result of said measurement output signal, said number detectormeans operating when said sensed digit is other than a predeterminedvalue to cause said measuring means to provide a measurement outputsignal to said count indication means until said sensed digit is alteredto said predetermined value.
 56. The electronic measuring unit of claim54 wherein said count indication means includes counter means operativein response to said measurement output signal to register a digitalvalue indicative of said measurement output signal during saidmeasurement cycle and output control means connected to receive anoutput from said counter means, said output control means operating toselectively provide an output representing either the numerical valueregistered by said counter means or a complement thereof, and zero setcontrol means connected to control said output control means, said zeroset control means being operative to cause said output control means toprovide an output representing only the complement of the numericalvalue registered by said counters, said zero test means operating whensaid sensed digits fall within a predetermined range of numerical valuesto initiate operation of said zero set control means.
 57. The electronicmeasuring unit of claim 56 wherein said zero test means activates saidautomatic zeroing means when said sensed digits fall within a firstpredetermined range of numerical values and activates said zero setcontrol means when said sensed digits fall within a second predeterminedrange of numerical values, said second range of numerical valuesdiffering from said first range.
 58. A method for obtaining aperiodically adjusted reference for use in electronic measuring whichincludes: obtaining a first signal value indicative of the output signalfrom a measuring means; storing said first signal value as a firstreference value for subsequent measuring means outputs; obtaining asubsequent second signal value indicative of a subsequent second outputsignal from said measuring means; obtaining the algebraic differencebetween said first and second signal values; comparing the algebraicdifference between said first and second signal values to apredetermined band of signal values; and storing said second signalvalue as a reference value for subsequent measuring means outputs whensaid algebraic difference is within said predetermined band.
 59. Themethod of claim 58 which includes retaining said first signal value as areference for subsequent measuring outputs when said algebraicdifference is not within said predetermined band of signal values. 60.The method of claim 59 which includes employing said second signal valueto provide a measurement indication.
 61. The method of claim 58 whichincludes periodically obtaining said second signal value and comparingthe algebraic difference between each said second signal value with thelast stored reference value.
 62. The method of claim 58 which includesvarying said predetermined band of signal values to vary the band withinwhich said second signal value is stored as a reference for subsequentmeasuring means outputs.
 63. The method of claim 58 which includesobtaining a first digital signal indicative of said first signal value,obtaining a second digital signal indicative of said second signalvalue, and comparing the algebraic difference between said first andsecond digital signals to a predetermined band of digital signals. 64.In an electronic measuring system having measuring means adapted toprovide a measurement output signal value which is a function of aquantity to be measured, a reference system comprising storage meansconnected to receive and store a measurement output signal value fromsaid measuring means, reference set means operative to cause saidstorage means to receive and store a first measurement output signalvalue from said measuring means as a first reference value, means toreceive said first reference value from said storage means and asubsequent second measurement output signal value from said measuringmeans and operative to provide a difference signal indicative of thealgebraic difference between said second measurement output signal valueand said first reference value, value determining means connected toreceive said difference signal and operative to determine whether saiddifference signal falls within a predetermined band of signal values,said value determining means operating when said difference signal fallswithin the predetermined band of signal values to initiate the storageof said second measurement output signal value in said storage means asa reference value for a subsequent measurement output signal.